A STUDY OF LIVING SUBSTANCE 



25 



We must now try to get a clear idea of what is meant by 

 the term cell, since a "knowledge of cell structure and cell 

 activity is absolutely essential for a clear understanding of 

 biology. If the amoeba is colored with certain stains, we 

 can see a darker spot in the center to which is given the 

 name cell nu'cle-us (Latin nucleus a small nut). The 

 rest of the animal is called its cell body. The living sub- 

 stance of which nucleus and cell body are composed is 

 now universally known 

 as pro'to-plasm. A cell, 

 therefore, in the biological 

 sense is a bit of protoplasm 

 containing a nucleus. 1 



Cells of the Blood. 

 Keeping in mind the 

 facts we have learned in 

 our study of the amoeba, 

 we will now return to 

 the structure of the hu- 

 man body. Let us first 

 examine with the micro- 

 scope a drop of fresh 

 blood. 2 We soon find 

 it is not the simple red 

 liquid it seems to be; 

 it consists of solid par- 

 ticles, called blood cor'pus-cles, floating in a watery liquid 



1 The term cell was first used in describing the structure of plants, 

 because in plant tissues the protoplasm is inclosed in little boxes or 

 rooms, the boundaries of which are called cell walls. The botanists 

 who first used the term cell noticed the walls before protoplasm 

 was discovered. The cell walls of plants are formed of cel'lu-lose, 

 a substance resembling starch. Many animal cells do not have a cell 

 wall. 



2 The blood can be easily obtained by tying a cord tightly about 

 the finger and then pricking it with a clean needle. A drop is 

 squeezed out upon a glass slide and covered with a thin cover glass. 



FIG. 6. Blood Corpuscles. 



a, 6 = white corpuscles (nucleus not 



seen). 



c, d, e white corpuscles (nucleus seen). 

 r = red corpuscles (surface view) . 

 r' red corpuscles (edge view) run 

 together in piles. 



